The causative link between nucleoside reverse transcriptase inhibitor (NRTI)-induced mitochondrial dysfunction and the development of HIV lipoatrophy is now well established. However, host immunologic and HIV virologic factors may contribute to its pathogenesis. We plan to assess their contribution through our central hypothesis that monocytes/macrophages (M/MOs) and HIV infection of such cells play key supporting roles in the pathogenesis of HIV lipoatrophy. Pro-inflammatory cytokines are increased in adipose tissue of lipoatrophic subjects. New data from several research laboratories including our own suggest 1) that adipose tissue M/MO levels are also increased in lipoatrophy and that 2) these M/MOs may be responsible for the high levels of cytokines in such adipose tissue. In a 5 cohort cross-sectional study (n=15/cohort), we propose to verify the increase in adipose tissue M/MOs in lipoatrophic subjects on zidovudine (ZDV)- or stavudine (d4T)-containing antiretroviral (ARV) regimens in comparison to 4 control groups (non-lipoatrophic patients on similar regimens, ARV-na'ive patients, subjects on Tenofovir- and/or Abacavir-containing regimens and HIV-seronegative controls). By assessing cytokines separately in adipocyte, pre-adipocyte and macrophage cellular components, we propose to establish that macrophages are the predominant source of cytokines in lipoatrophic subjects. We will expore the relationships that exist between adipose tissue M/MOs, cytokines, parameters of mitochondrial dysfunction and apoptosis. Finally, we believe that M/MO infiltration is enhanced by HIV infection of such cells in the bloodstream. We will confirm our recent report that lipoatrophy is associated with high levels of HIV infection (HIV DNA) within peripheral blood mononuclear cell (PBMC), and test the hypothesis that this high HIV DNA is found predominantly within the M/MO fraction of PBMCs rather than within lymphocytes. We will conduct these assessments not only in our local cohort but within serially banked PBMCs from selected subjects (n=100) who participated in AIDS Clinical Trials Group (ACTG) A5095, a recently completed large multi-center ARV trial in ARV-naive subjects. The attractiveness of this cohort lies in the ability to objectively identify lipoatrophy through change over time in arm and thigh circumferences. We are particularly well suited to undertake these studies as our research team combines clinical research expertise in HIV lipoatrophy with specific laboratory competency in adipose tissue-, mitochondrial- and M/MO-related research.